On Mon, 27 Mar 2023 at 23:10, Alex Bennée <alex.ben...@linaro.org> wrote:
>
>
> Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk> writes:
>
> > On 27/03/2023 17:12, Alex Bennée wrote:
> >
> >> Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk> writes:
> >>
> >>> On 27/03/2023 14:15, Alex Bennée wrote:
> >>>
> >>>> I'm still not sure how I achieve by use case of the parent class
> >>>> defining the following properties:
> >>>> static Property vud_properties[] = {
> >>>> DEFINE_PROP_CHR("chardev", VHostUserDevice, chardev),
> >>>> DEFINE_PROP_UINT16("id", VHostUserDevice, id, 0),
> >>>> DEFINE_PROP_UINT32("num_vqs", VHostUserDevice, num_vqs, 1),
> >>>> DEFINE_PROP_END_OF_LIST(),
> >>>> };
> >>>> But for the specialisation of the class I want the id to default to
> >>>> the actual device id, e.g.:
> >>>> static Property vu_rng_properties[] = {
> >>>> DEFINE_PROP_UINT16("id", VHostUserDevice, id, VIRTIO_ID_RNG),
> >>>> DEFINE_PROP_UINT32("num_vqs", VHostUserDevice, num_vqs, 1),
> >>>> DEFINE_PROP_END_OF_LIST(),
> >>>> };
> >>>> And so far the API for doing that isn't super clear.
> >>>> Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
> >>>> ---
> >>>> include/hw/qdev-core.h | 9 +++++++++
> >>>> 1 file changed, 9 insertions(+)
> >>>> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> >>>> index bd50ad5ee1..d4bbc30c92 100644
> >>>> --- a/include/hw/qdev-core.h
> >>>> +++ b/include/hw/qdev-core.h
> >>>> @@ -776,6 +776,15 @@ BusState *sysbus_get_default(void);
> >>>> char *qdev_get_fw_dev_path(DeviceState *dev);
> >>>> char *qdev_get_own_fw_dev_path_from_handler(BusState *bus,
> >>>> DeviceState *dev);
> >>>> +/**
> >>>> + * device_class_set_props(): add a set of properties to an device
> >>>> + * @dc: the parent DeviceClass all devices inherit
> >>>> + * @props: an array of properties, terminate by
> >>>> DEFINE_PROP_END_OF_LIST()
> >>>> + *
> >>>> + * This will add a set of properties to the object. It will fault if
> >>>> + * you attempt to add an existing property defined by a parent class.
> >>>> + * To modify an inherited property you need to use????
> >>>> + */
> >>>> void device_class_set_props(DeviceClass *dc, Property *props);
> >>>> /**
> >>>
> >>> Hmmm that's an interesting one. Looking at the source in
> >>> hw/core/qdev-properties.c you could possibly get away with something
> >>> like this in vu_rng_class_init():
> >>>
> >>> ObjectProperty *op = object_class_property_find(klass, "id");
> >>> object_property_set_default_uint(op, VIRTIO_ID_RNG);
> >>>
> >>> Of course this is all completely untested :)
> >> Sadly we assert on the existing prop->defval:
> >> static void object_property_set_default(ObjectProperty *prop,
> >> QObject *defval)
> >> {
> >> assert(!prop->defval);
> >> assert(!prop->init);
> >> prop->defval = defval;
> >> prop->init = object_property_init_defval;
> >> }
> >> Maybe the assert is too aggressive or we need a different helper,
> >> maybe
> >> a:
> >> void object_property_update_default_uint(ObjectProperty *prop,
> >> uint64_t value)
> >> ?
> >
> > It seems in that case once the default has been set, it is impossible
> > to change. The only other immediate option I can think of is to define
> > a specific DEFINE_VHOST_PROPERTIES macro in a similar way to
> > DEFINE_AUDIO_PROPERTIES which you can use to set the common properties
> > for all VHostUserDevice devices, including providing the default ID.
>
> I tried this: allow the default to change
>
> modified qom/object.c
> @@ -1557,11 +1557,16 @@ static void object_property_init_defval(Object *obj,
> ObjectProperty *prop)
>
> static void object_property_set_default(ObjectProperty *prop, QObject
> *defval)
> {
> - assert(!prop->defval);
> - assert(!prop->init);
> + if (prop->init == object_property_init_defval) {
> + fprintf(stderr, "%s: updating existing defval\n", __func__);
> + prop->defval = defval;
> + } else {
> + assert(!prop->defval);
> + assert(!prop->init);
>
> - prop->defval = defval;
> - prop->init = object_property_init_defval;
> + prop->defval = defval;
> + prop->init = object_property_init_defval;
> + }
> }
I think this leaves the door open to bugs where you create
the property, somebody looks at it, and then you update
the default value afterwards...
-- PMM
